Composite structure and production method thereof

ABSTRACT

A composite structure comprising a metallic sheet and two thermoplastic material layers of a layer (A) and a layer (B) which are placed in turn and integrated with each other, characterized in that the layer (A) comprises a thermoplastic material capable of being thermally fusedly adhered to the thermoplastic material in the layer (B), the metallic sheet and the layer (A) are adhered to each other, and the layers (A) and (B) are thermally fusedly adhered to each other; and a process for producing a composite structure which comprises installing, on a metallic sheet by coating, a layer (A) comprising a thermoplastic material capable of being thermally fusedly adhered to a thermoplastic material in a layer (B) to be placed thereon, and further installing the layer (B) on the layer (A) by thermally fusedly adhering a desirable thermoplastic material on the (A).

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a composite structure whichcomprises a metallic sheet and thermoplastic materials and a process forthe production of said composite structure. More particularly, thepresent invention is concerned with a composite structure which is wellsuited for use in a gasketed cover and the like to be used for housingelectronic equipment, etc. and in which an injection moldedthermoplastic material is integrated with a metallic sheet withfavorable adhesivity by coating the metallic sheet in advance, with anadhesive; and a process for readily and efficiently producing saidcomposite structure.

[0003] 2. Description of the Related Arts

[0004] The development of electronic equipment in recent years reallyamazes the persons concerned. The aforesaid equipment, which issubjected to printed circuit on a substrate by the use of integratedcircuits utilizing semiconductors, is directed to compactifiedlightweight equipment, and is prone to be readily damaged by moisture ordampness in particular. Accordingly, the hermetically sealing propertiesof a case housing electronic equipment is a factor of importance for theperformance and durability of the electronic equipment.

[0005] The case housing electronic equipment is constituted of a boxbody and a cover body, which are integrated by interposing on thejointing surface thereof, a gasket made of vulcanized rubber, a urethanefoam and a thermoplastic material or the like. The gasket is usually inthe form of a gasket which is fitted to a cover body and thus fixed tothe cover, but there is unavailable a favorable method of adhesivelybonding the gasket to the cover body. Accordingly, the fixation iscarried out by a (1) method comprising fixing the gasket on the coverbody by means of a double-coated tape, a (2) method comprising makingholes in the cover body and fixing a gasket material from both sides ofthe cover body through the holes, or the like method. The gasketed coverbody is fixed on a box body by means of screws and accordingly, thefixing job is markedly facilitated by the adhesion of the gasket to thecover body.

[0006] As the above-mentioned (1) method comprising fixing the gasket onthe cover body by means of a double-coated tape, there is usuallyadopted a method in which a sheet like gasket material to which adouble-coated tape is adhered, is punched into a shape of gasket, andthe resultant gasket is fixed to the cover body. However, said method isinvolved in such problems that most of the sheet-like gasket materialafter punching remains as waste material and besides, the productionprocess is made intricate or troublesome, thus inevitably increasing theproduction cost, since the gasket is fixed to the cover body after thegasket material has been punched into a shape of gasket.

[0007] In addition, in the (2) method comprising making holes in thecover body and fixing a gasket material through the holes, since thegasket material is exposed on the upper side of the cover body, thegasket material exposed thereon is sometimes upturned or curled when thecover body is inserted into the space of an electronic equipment mainbody, said space being narrowed accompanying the recent compactifiedelectronic equipment part items. Thus, there is caused the problem thatsuch upturning or curling is responsible for defective sealingproperties.

[0008] Moreover, in the case where the gasket which is fitted to a coverbody and which is produced by such a method, is used in a hard discunit, there is caused the problem that it is impossible to suppress thevibration due to the rotation of the hard disc.

[0009] On the one hand, the adhesion between a thermoplastic materialand a metallic sheet as the cover body, is usually carried out by amethod in which the thermoplastic material is subjected to adhesiontreatment on the surface thereof by corona discharge or the like, andthereafter is stuck to the metallic sheet by using an epoxy-based or aurethane-based adhesive. Nevertheless, the job in said method isintricate and troublesome, and is involved in gas generation problem,whereby the method is inapplicable to a gasket for use in electronicequipment.

[0010] In order to simplify and facilitate the aforesaid job,consideration is given to a method comprising injection molding anadhesive thermoplastic material for the purpose of direct adhesion.However, such a thermoplastic material, even when being made ratherhard, is enlarged upon injection molding, thereby making it impossibleto employ the molded product as such as a gasket. Therefore, said methodhas not been adopted to the production of a gasket for a cover body in ahard disc.

SUMMARY OF THE INVENTION

[0011] Under such circumstances, it is a general object of the presentinvention to provide a composite structure which comprises a metallicsheet and a thermoplastic material that are integrated in good adhesionby injection molding, and which is excellent in such a performance asvibration-damping properties and is well suited for usage in a gasketfitted to a cover body to be used for housing electronic equipment andthe like.

[0012] Other objects of the present invention will be obvious from thetext of the specification hereinafter disclosed.

[0013] In view of the foregoing, intensive extensive research andinvestigation were accumulated by the present inventors in order todevelop the above-mentioned composite structure having favorableproperties. As a result, it has been found that the general object canbeen achieved by the composite structure which is equipped, on ametallic sheet by coating, with a layer comprising a thermoplasticmaterial capable of being thermally fusedly adhered to a thermoplasticmaterial to be placed thereon, and further equipped on said layer with alayer comprising a desirable thermoplastic material by means of thermalfusion adhesion. It being so, the present invention has beenaccomplished on the basis of the above-mentioned findings andinformation.

[0014] Specifically, the present invention provides a compositestructure comprising a metallic sheet and two thermoplastic materiallayers of a layer (A) and a layer (B) which are placed in turn andintegrated with each other, characterized in that said layer (A)comprises a thermoplastic material capable of being thermally fusedlyadhered to the thermoplastic material in the layer (B), said metallicsheet and said layer (A) are adhered to each other by coating, and saidlayers (A) and (B) are thermally fusedly adhered to each other. Thepresent invention further provides a process or producing a compositestructure which comprises installing, on a metallic sheet by coating, alayer (A) comprising a thermoplastic material capable of being thermallyfusedly adhered to a thermoplastic material in a layer (B) to be placedthereon, and further installing the layer (B) on said layer (A) bythermally fusedly adhering a desirable thermoplastic material on saidlayer (A).

BRIEF DESCRIPTION OF THE DRAWING

[0015]FIG. 1 is a perspective illustration which shows one example of agasket fitted to a cover body according to the present invention,wherein the symbols 1 and 2 denote gasket and cover body, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The composite structure according to the present inventioncomprises a metallic sheet and two thermoplastic material layers of alayer (A) and a layer (B) which are placed in turn and integrated witheach other.

[0017] The above-mentioned metallic sheet is not specifically limited,but can be properly selected for use according to the purpose of use ofthe composite structure, from cold rolled steel sheets, galvanized steelsheets, aluminum/zinc alloy plated steel sheets, stainless steel sheets,aluminum sheets, aluminum alloy sheets, magnesium sheets and magnesiumalloy sheets, and the like.

[0018] There is preferably usable a metallic sheet which is treated withnon-electrolytic nickel plating for its being inexpensive and excellentin corrosion resistance. As a method for non-electrolytic nickelplating, there is usable any of well known methods that have heretoforebeen applied to metallic raw materials, for instance, a method whichcomprises immersing a metallic sheet to be treated in a non-electrolyticnickel plating bath comprising an aqueous solution at a pH ofapproximately 4.0 to 5.0 and at a temperature of approximately 85 to 95°C. which contains nickel sulfate, sodium hypochlolite, lactic acid,propionic acid and the like each in a proper proportion.

[0019] The thickness of the metallic sheet to be employed in the thepresent invention is properly selected for use according to the purposeof use of the composite structure, and is in the range of usually from0.1 to 2 mm, preferably from 0.2 to 1 mm.

[0020] The layer (A) is a layer comprising a layer capable of beingthermally fusedly adhered to the thermoplastic material in the layer (B)to be equipped thereon. The thermoplastic material in the layer (A) isproperly selected for use according to the type of the thermoplasticmaterial to be used in the layer (B), for instance, from polyolefinicresin, polystyrenic resin, acrylic resin and the like. In the case wherea styrenic thermoplastic elastomer is used in the layer (B), it isadvantageous to use a modified polyolefinic resin as a thermoplasticmaterial in the layer (A). In this case, the polyolefinic resin isexemplified by a homopolymer of an α-olefin such as ethylene; propylene;butene-1; 3-methylpentene 1; and 4-methylpentene-1, a copolymer of atleast two in these, and a copolymer of any of these and an otherpolymerizable unsaturated monomer. Typical examples thereof includeethylenic polymer such as high density, intermediate density and lowdensity polyethylenes, straight-chain low density polyethylene,ethylene/vinyl acetate copolymer and ethylene/ethyl acrylate copolymer,propylenic polymer such as propylenic homopolymer, propylene/ethyleneblock or random copolymer, propylene/ethylene/diene compound copolymer,polybutene-1; and poly 4-methylpentene-1.

[0021] In order to enhance the adhesivity to the metal, there areeffectively usable the above-mentioned resins incorporated with an acidanhydride, a functional group such as carboxyl group, carboxylic acidester group or chlorosulfonate group, or a halogen.

[0022] The layer (A) in the present invention is installed onto themetallic sheet in good adhesion by means of coating. In this case, thecoating is carried out usually at a temperature close to the softeningpoint or melting point of the thermoplastic material to be used. Thethickness of the layer (A) is selected in the range of usually from 3 to100 μm, preferably from 5 to 30 μm.

[0023] In the composite structure according to the present invention, athermoplastic material layer as the layer (B) is formed on the layer (A)by means of thermal fusion adhesion. The thermoplastic material whichconstitutes the layer (B) is not specifically limited, but can beproperly selected for use from various materials according to thepurpose of use of the composite structure.

[0024] In the case where, for instance, the composite structure is usedas a sealing member, and the gasket portion is the layer (B), thethermoplastic material which constitutes the layer (B) is preferably athermoplastic material having a low hardness of less than 60 degrees interms of JIS hardness A. Examples of said thermoplastic material havinga low hardness include thermoplastic elastomers of styrenic base,olefinic base, urethane based and acrylic base, respectively. Inparticular, with regard to a case for housing electronic equipment, itis preferable to use such a material that surely interrupts moisture andair and besides does not generate a halogen base gas or an acidic gas.From the viewpoint of adhesivity to the box body of a case andtackiness, it is preferable to use a material having a JIS hardnessbeing less than 60 degrees, especially being in the range of 15 to 45degrees. The above-mentioned thermoplastic material is preferably athermoplastic elastomer of styrenic base, which is exemplified bystyrene/butadiene/styrene block copolymer (SBS), hydrogenatedstyrene/butadiene/styrene block copolymer (SEBS), styrene/isoprene blockcopolymer (SIR), styrene/isoprene/styrene block copolymer (SIS) andhydrogenated styrene/isoprene/styrene block copolymer (SEPS).

[0025] Specific examples of the foregoing styrenic thermoplasticelastomer include “Rubberon” manufactured by Mitsubishi ChemicalIndustries Co., Ltd., specifically exemplified by “Rubberon MJ4300B”(trade name) having a JIS hardness A of 15 degrees and “Rubberon T320C”(trade name) having a JIS hardness A of 15 degrees, “Septon”manufactured by Kuraray Co., Ltd., specifically exemplified by “Septon2063” (trade name) having a JIS hardness A of 36 degrees, and “ElastomerAR” manufactured by Aron Kasei Co., Ltd. Different from EPDM and butylrubber, the styrenic thermoplastic elastomer need not vulcanization andcan be recycled, thereby greatly contributing to cost curtailment.Specific examples of the olefinic thermoplastic elastomer include“Santprene” manufactured by A. E. S. Japan Inc. (trade name) having aJIS hardness A of 45 degrees.

[0026] The thermoplastic material which constitutes the layer (B) may beused alone or in combination with at least one other.

[0027] With respect to the composite structure according to the presentinvention, the thickness of the layer (B) to be placed on the aforesaidlayer (A) by means of thermal fusion adhesion is not specificallylimited, but can be properly selected for use in accordance with thepurpose of use of the composite structure, and it is in the range ofusually 0.1 to 5 mm, preferably 0.2 to 2 mm.

[0028] It is possible in the present invention that the thermoplasticmaterial layer as the layer (B) be incorporated, as desired and to theextent that the objects of the present invention are not impaired, withsuch additives as an anti-oxidants (age resisters), ultravioletabsorbers, light stabilizers and a variety of fillers specificallyexemplified by carbon black, talc, barium sulfite, calcium carbonate,magnesium carbonate, metal oxide, mica, graphite, aluminum hydroxide,various metallic powders, wood chipping, glass powder, ceramic powder,granular or powdery polymer, glass fiber, metallic fiber, and organicfiber.

[0029] Particularly preferably usable composite structure in the presentinvention, is that comprising a styrenic thermoplastic elastomer as thelayer (B) and a polyolefinic thermoplastic elastomer as the layer (A).

[0030] The process for producing the composite structure according tothe present invention is not specifically limited, provided that saidprocess is capable of producing the composite structure imparted withthe above mentioned properties. According to the simplified process ofthe present invention as described hereunder, it is made possible toefficiently produce a desirable composite structure.

[0031] In the process according to the present invention, first of all,the layer (A) is formed on a metallic sheet which has been preferablysubjected to non-electrolytic nickel plating by coating the metallicsheet with a thermoplastic material (hereinafter sometimes referred toas “thermoplastic material I”), capable of being thermally fusedlyadhered to the thermoplastic material in the layer (B) (hereinaftersometimes referred to as “thermoplastic material II”) to be placed onthe layer (A). The metallic sheet or the metallic sheet which has beensubjected to non-electrolytic nickel plating may be subjected at need,to a surface treatment such as plasto-treatment, treatment by hair line,etching, crack plating, oxidation, anodic oxidation, corona discharge,plasma or primer coating.

[0032] The layer (A) may be formed by the use of an aqueous emulsion ofthe thermoplastic material I from the standpoint of environmentalconcern or suppression of gas generation. Specifically in this case, thelayer (A) may be formed by pulverizing the thermoplastic material I suchas polyolefinic resin and emulsifying the resultant pulverized materialwith an emulsifier according to a previously well known method toprepare an aqueous emulsion containing the thermoplastic material I, andapplying coating of the resultant emulsion. In this case, an adhesivecomponent with good adhesivity of urethane base or epoxy base may beadded thereto as required, to the extent that the objects of the presentinvention are not impaired thereby.

[0033] Subsequently, by applying the solution of the modified adhesivepolyolefinic resin onto the metallic sheet so that the thickness of theresultant coating comes to be a desired value by a well known methodsuch as brush coating, padding coating, spray coating, roller coatingand flow coating, followed by drying, the layer (A) is formed adhesivelyonto the metallic sheet.

[0034] It is preferable to apply the solution of the modified adhesivepolyolefinic resin only to the portion where the gasket material isadhered by means of a dispenser, pat printing, screen printing or thelike from the viewpoint of preventing gas generation and curtailing themanufacturing cost.

[0035] Subsequently, by thermally fusedly adhering a desiredthermoplastic material II, for instance, styrenic thermoplasticelastomer or the like onto the layer (A) so as to form the layer (B). Inthe formation of the layer (B), there is preferably used injectioninsertion method, whereby for instance, a metallic sheet equipped withthe layer (A) is arranged in a mold, and the thermoplastic material IIis injectedly poured onto said layer (A) so that the thermoplasticmaterial II and the thermoplastic material I are thermally fusedlyadhered to each other to form the layer (B) having a desired thicknesson the layer (A). Alternatively, there is usable a method in which thelayer (B) is formed onto the layer (A) by thermally fusedly adhering thelayers by means of pressing method.

[0036] The thermal fusion adhesion temperature is properly selectedaccording to the types of the thermoplastic material I and thethermoplastic material II. In the case, for instance, wherepolypropylene is used as the thermoplastic material I and SEBS or SEPS,that is, styrenic thermoplastic elastomer is used as the thermoplasticmaterial II, said temperature is in the range of approximately 170 to200°.

[0037] In such a manner as described hereinbefore, there is obtainablethe composite structure according to the present invention wherein themetallic sheet and the thermoplastic materials are integrated with oneanother.

[0038] According to the process of the present invention, it is madepossible to readily integrate the thermoplastic material for a gasketand the metallic sheet through injection molding only by applying inadvance, the solution of an adhesive resin without deteriorating thephysical properties of the thermoplastic material. Further, thecomposite structure according to the present invention is excellent invibration-damping properties, since the metallic sheet is laminated withthe thermoplastic material I, and it is well suited for usage in thegasket fitted to a cover body to be used in sealing members,particularly electronic equipment.

[0039] Moreover according to the present invention, it is made possibleto prevent the adhesion of dirt such as dust and the leak ofelectromagnetic wave by mixing an electroconductive material in thethermoplastic material I and/or the thermoplastic material II, andbesides to prevent heat accumulation in a hard disc by by mixing amaterial having high heat releasabity in the thermoplastic material I soas to enable to release internally generated heat to the outside.

[0040] As described hereinbefore, the composite structure according tothe present invention, wherein the metallic sheet and thermoplasticmaterials are integrated with one another in good adhesivity by applyingin advance the adhesive resin onto the metallic sheet, and theninjection molding the thermoplastic gasket material, is excellent invibration-damping properties, and is is well suited for usage in thegasket fitted to a cover body to be used in electronic equipment and thelike.

[0041] Furthermore, the production process according to the presentinvention enables to efficiently produce the composite structure,dispensing with intricate or troublesome steps.

[0042] In what follows, the present invention will be described infurther detail with reference to comparative examples and workingexamples, which however shall never limit the present invention thereto.

EXAMPLE 1

[0043] An aluminum sheet which had a thickness of 0.5 mm and which wasequipped with non-electrolytic nickel plated film of μm in thickness wascoated thereon with a solution of a modified adhesive polyolefinic resin(maleic acid-modified copolymer of propylene, ethylene and butene,manufactured by Mitsubishi Chemical Industries Ltd. under the trade name“Unistol P-802”), and the resultant coated sheet was heat treated at 50°C. to prepare an aluminum sheet having the coated film of 30 μm inthickness.

[0044] Subsequently, onto the resultant adhesive polyolefinic resin coatformed on the aluminum sheet, there was insertion molded a styrenicthermoplastic elastomer having a JIS hardness A of 45 degrees(manufactured by Mitsubishi Chemical Industries Ltd. under the tradename “Rubberon MJ 4300B”) in a thickness of 0.5 mm by the use of aninjection molding machine under the temperature conditions of the nozzleand cylinder at 180° C. and the insert aluminum sheet at roomtemperature to prepare a composite structure.

[0045] The composite structure thus obtained was subjected to peel testfor styrenic thermoplastic elastomer in accordance with JIS Z 0237. As aresult, there were found the destruction of the material of thethermoplastic elastomer itself along with the delamination on theinterface between the aluminum sheet and the adhesive polyolefinic resincoat. However, the peeling strength at the time of delamination was atleast 1.6 kg/25 mm, thus showing sufficient adhesion strength for fixingthe composite structure to the main body by means of screws.

COMPARATIVE EXAMPLE 1

[0046] The procedure in Example 1 was repeated except that the adhesivepolyolefinic resin coat was not formed on the aluminum sheet subjectedto non-electrolytic nickel plating, namely the styrenic thermoplasticelastomer was directly insertion molded onto the aluminum sheet. As aresult, because of failure in adhesion, the elastomer was separated fromthe aluminum sheet at the time of taking out thereof.

EXAMPLE 2

[0047]FIG. 1 is a perspective illustration which shows a gasket fittedto a cover to be used for a case housing a hard disc drive unit as oneembodiment of the composite structure according to the presentinvention, and which is viewed from the sealing surface side, wherein agasket 1 is adhered to the surface of a metallic cover body 2 as a coverfor the case housing a hard disc drive unit. Such equipment andmachinery as a magnetic disc, a magnetic head and an actuator arearranged in the box body side of the case housing a hard disc driveunit, closed with said box body (not illustrated on the drawing) andsaid gasket fitted to the cover, and are housed in said case.

[0048] As the cover body 2, use was made of an aluminum sheet which hada thickness of 0.5 mm and which was equipped with non-electrolyticnickel-plated film of 5 μm in thickness, was coated thereon with asolution of a modified adhesive polyolefinic resin (maleic acid-modifiedadhesive polypropylene, manufactured by Mitsubishi Chemical IndustriesLtd. under the trade name “Unistol R-300”), and the resultant coatedsheet was heat treated in the same manner as in Example 1 to prepare analuminum sheet with the coated film of 30 μm in thickness.

[0049] Subsequently, onto the resultant polypropylene coat formed on thealuminum sheet, there was insertion molded a styrenic thermoplasticelastomer in a thickness of 0.5 mm in the same manner as in Example 1 toform the gasket 1 and prepare a gasket fitted to a cover. As the resultof peel test in accordance with JIS Z 0237, the peeling strength at thetime of delamination was at least 1.4 kg/25 mm, thus showing sufficientadhesion strength for fixing said gasket to the main body by means ofscrews.

[0050] The gasket fitted to a cover thus prepared was used as the coverof the case housing a hard disc drive unit for a period of 30 days sothat the gasket portion faced the box body, and thereafter visualobservation was made of the gasket portion. As a result, the dustpreventive properties during the service was satisfactory withoutobservable sagging on the gasket portion. Further observation was madeof the vibration-damping performance of the gasket fitted to a cover inthe hard disc drive unit. As a result, resonance due to the hard discwas not observed.

COMPARATIVE EXAMPLE 2

[0051] The procedure in Example 2 was repeated except that the modifiedadhesive polyolefinic resin coat was not formed on the aluminum sheet.Thus, there was prepared a gasket fitted to a cover by injection moldinga styrenic thermoplastic elastomer onto a cover body having holes forfixing said elastomer. Then, observation was made of thevibration-damping performance of the gasket fitted to a cover in thehard disc drive unit. As a result, resonance due to the hard disc wasobserved.

[0052] As is obvious from the foregoing results of evaluations, thegasket fitted to a cover as one of the embodiments of the presentinvention, can readily be produced, exhibits favorable dust preventiveproperties owing to good adhesion between the gasket and the cover bodywhen used as a cover of a case housing a hard disc drive unit, andbesides is free from any deformation even after a long time of servicebecause of the gasket being constituted of a material having a lowhardness.

What is claimed is:
 1. A composite structure comprising a metallic sheetand two thermoplastic material layers of a layer (A) and a layer (B)which are placed in turn and integrated with each other, characterizedin that said layer (A) comprises a thermoplastic material capable ofbeing thermally fusedly adhered to the thermoplastic material in thelayer (B), said metallic sheet and said layer (A) are adhered to eachother, and said layers (A) and (B) are thermally fusedly adhered to eachother.
 2. The composite structure according to claim 1, wherein thelayer (A) comprises a modified polyolefinic resin, and the layer (B)comprises a styrenic thermoplastic elastomer.
 3. The composite structureaccording to claim 1, wherein the metallic sheet is that subjected tonon-electrolytic nickel plating.
 4. The composite structure according toclaim 1, which is used as a sealing member.
 5. The composite structureaccording to claim 4, wherein the sealing member is a gasket fitted to acover for a hard disc drive.
 6. A process for producing a compositestructure which comprises installing, on a metallic sheet by coating, alayer (A) comprising a thermoplastic material capable of being thermallyfusedly adhered to a thermoplastic material in a layer (B) to be placedthereon, and further installing the layer (B) on said layer (A) bythermally fusedly adhering a desirable thermoplastic material on saidlayer (A).